The need for engaging and disengaging a drive and driven shaft is particularly prevalent in vehicles that are shifted between two-wheel drive and four-wheel drive. Typically, a front wheel drive (or propeller) shaft extends from a vehicle's transfer case (or transmission) to a front wheel differential and a rear wheel drive (or propeller) shaft extends from the transfer case to a rear wheel differential. Axles extend from each differential to the respective right and left wheels. These components are sometimes collectively referred to as the vehicle's drive line. A clutch ring may be provided at any or several of a number of different locations between and inclusive of the transfer case (transmission) and wheel hubs. Typically either the rear wheels are permanently engaged or the front wheels are permanently engaged and that portion of the drive line does not likely include a clutch ring. It is the case, however, that a clutch ring is provided at or in the transfer case as well as at the wheel hubs of the disengageable wheels. Disengagement of both renders the drive line components between the wheel and transfer case inactive. Should the drive line be disengaged at the transfer case and not the wheel hubs, the components will be rotated by their connection to the wheel. Alternatively, the axles are disengaged from the propeller shaft at the differential (referred to as a center disconnect). The axles are still driven by the wheel but the propeller shaft (having the greater mass) is rendered inactive.
The clutch ring is shifted between positions of engagement and disengagement by actuators. Actuators can be mechanical (manual shift or automatic shift using cams) or they can be air actuated, hydraulic actuated or electric actuated. The present invention is directed to an electric actuator for a clutch ring.
An electric powered actuator as contemplated herein is provided with an electric motor connected to a shift fork which in turn is connected to a clutch ring. Whereas an electric motor, by design, will move a component between two precise positions, when energized it must be allowed to move the component to which it is connected fully between these positions. The clutch ring on the other hand cannot be required to move an exact distance at a given time as the clutch ring has to line up with the engagement features, i.e., splines on the component to which it is to be engaged. A delay must be permitted to allow for alignment. Accordingly, the fork or associated components of the fork must be constructed to permit such a delay. Whereas the above refers to an engagement problem, a similar problem occurs during disengagement. When attempting to disengage while the components are under high torque, movement of the clutch ring is strongly resisted due to frictional resistance, sometimes referred to as torque lock up or torque lock. Whereas the alignment problem is most commonly referred to herein, the solutions to that problem similarly apply to torque lock up occurring during disengagement.
The present invention is intended to optimize the construction of an electric powered actuator under the conditions as described above.